Is it permissible for a man to buy land belonging to a mosque that was demolished by a communist government and seized by it, and then build upon it, despite his knowledge that it is a waqf (endowment), and is he sinful for doing so?

"Whoever bought an endowed land from an usurping state has committed a great wrong and a sin, for the Prophet, peace and blessings be upon him, said: 'Whoever usurps a hand span of land unjustly, Allah will encircle his neck with it on the Day of Resurrection from seven earths.' And whoever takes from the usurper is like the usurper. He must be advised to repent to Allah, return the land to the endowment, and try to recover his money. If he cannot, then let him be sincere in his repentance, perhaps Allah will compensate him with something better, for Allah the Almighty says: 'And whoever fears Allah – He will make for him a way out And will provide for him from where he does not expect.'"